1. Field of the Invention
The present invention relates to a vessel propulsion system using an engine, preferably an internal combustion engine, as a propulsive force generation source.
2. Description of the Related Art
United States Patent Application Publication No. US 2002/0177940 A1 discloses an outboard motor with which a propulsion unit is driven by an internal combustion engine. A throttle valve is disposed in an air intake passage of the internal combustion engine. Also, a bypass passage introduces air from the atmosphere into an air intake passage further downstream of the throttle valve. An opening/closing valve that can be adjusted in its opening degree is interposed in the bypass passage. During starting of the internal combustion engine, the opening degree (bypass opening degree) of the opening/closing valve is controlled according to an engine temperature and after completion of warm-up of the engine, the bypass opening degree is controlled to attain a predetermined idling engine speed. To obtain a desired trolling propulsion state, a portable terminal is connected to the control unit and arrangements are made to enable a larger value or a smaller value than the idling engine speed to be set as a target engine speed. The desired trolling propulsion state can thereby be obtained by increasing/decreasing the target engine speed in a stepwise manner based on the idling engine speed.